1. Field of the Invention
The present invention relates to a valve lifter rocker arm for an internal combustion engine.
2. Background Art
Valves for internal combustion engines are generally opened and closed to allow for the intake and exhaust of gases in cylinders of the engine. Valves are operated by various valve lifter mechanisms including rocker arms and roller finger follower assemblies. Timing valve opening and closing is important to maximize fuel efficiency, assure complete combustion, and maximize engine output. Adjusting valve timing can lead to improvements in fuel economy, engine emissions, torque and idle quality.
Many different approaches have been proposed for providing adjustable valve timing. Some prior art approaches include independent lifter control for each cylinder by means of electrical solenoids or by changing the pivot point for a rocker arm. Various other approaches have also been proposed.
There is a need for a system and apparatus for providing adjustable valve timing wherein the valve timing may be adjusted in a synchronized manner to minimize variation of timing from cylinder to cylinder. There is also a need for a simple and effective valve timing adjustment mechanism that may be used with intake or exhaust valves. There is also a need for a valve timing adjustment mechanism that is amenable to dual overhead cam and single overhead cam applications. There is a further need to provide a simple and effective way to deactivate cylinders by deactivating valve lifter operation selectively when a cylinder is not firing pursuant to a variable displacement engine operation strategy.
The above problems and objectives are addressed by the present invention as summarized below.
According to one aspect of the present invention, a valve timing system for an internal combustion engine having a rotating cam that operates at least one valve is provided. A rocker arm is pivotally attached to the engine. The rocker arm has a cam arm extending toward the rotating cam and a valve arm that contacts a valve stem. A cam roller is attached to the cam arm and is adjustable within a range of positions along the length of the cam arm. The cam roller is supported on the cam arm to selectively contact the rotating cam. A linkage is connected to the cam roller and the rocker arm. The linkage is used to adjust the position of the cam roller to change the timing of the valve of the engine.
According to another aspect of the present invention, a rocker arm assembly is provided for an internal combustion engine. The engine has at least one valve that is opened and closed in a timed manner to port combustion gases for a combustion chamber of the internal combustion engine. The internal combustion engine has at least one cam shaft and at least one cam that is rotated by the cam shaft in accordance with the operating cycle of the internal combustion engine. The cam has a lobe that is rotated to contact the rocker arm assembly to open and close the valve. The rocker arm assembly comprises a rocker arm pivotally secured to the engine that has a valve stem engaging arm and a cam engaging arm on opposite its ends. A roller is adjustably secured to the cam engaging arm and is held on the cam engaging arm in a position to contact the cam as it is rotated by the cam shaft. An adjustment link is provided for shifting the roller relative to the cam engaging arm to cause the roller to contact the lobe of the cam within a range of rotational positions relative to the cam shaft.
Other features of the invention include providing a cam arm that has a pair of spaced flanges between which the cam roller is secured. The cam roller is preferably rotatably secured to the cam arm. The cam roller may be secured to the cam arm by a shaft that extends through a slot formed in the cam arm.
The linkage comprises an adjustment link and a cam roller that is secured to the cam arm by a shaft that is engaged by one end of the adjustment link. The linkage may comprise at least one adjustment cam that is attached to an adjustment control shaft and the adjustment link. The adjustment control shaft may be rotated to rotate the adjustment cam relative to the rocker arm to cause the adjustment link to move the cam roller on the cam arm.
A bushing may be mounted on the adjustment control shaft and secured to the rocker arm wherein the bushing is rotatable relative to the adjustment control shaft and the rocker arm mounting shaft.
According to another aspect of the invention, the slot formed in the cam arm extends generally lengthwise relative to the cam arm. The one end of the slot in the cam arm may be curved away from the rotating cam so that the cam roller may be moved to a recessed position on the cam arm in which the cam roller does not contact the rotating cam.
These and other aspects of the valve timing system and rocker arm assembly of the present invention will be better understood in view of the attached drawings and following detailed description of the preferred embodiments of the invention.